Over 60% of carbon dioxide (CO2) sent to the atmosphere
comes from fired heaters and utility or industrial power
systems based on fossil-fuel combustion.1 The industrial
capture of CO2 from emissions is possible with low
pressure solvent absorption, a simple process operation that
becomes particularly important for combustion furnaces, burners
and incinerators. Traditionally, the absorption of acidic gases
has been done under pressure with amine solutions, but
typical combustion flue gases have large flowrates. Inert N2 is
the bulk constituent and CO2 is generally diluted to
10% vol15% vol. Fig. 1 shows the example of a tenfold
polytropic compression at the 80% optimistic efficiency for
100,000 Nm3/h, a relatively small industrial gas flowrate. The
compression requires 12 MWh or 3.2 kW per kmole of gas and
determines a net loss, in spite of the power that can be
recovered through a turbine expander, located on the lighter
CO2-free gas returning from the absorber, and the
heat recuperated from various intercoolers plus the reheated
gases to the chimney. Higher losses are incurred if the gas is
compressed to 4,000 kPa or more, for deepsea or sealed-cavern
remote confinement, possibilities that lead to comparing
CO2 sequestering costs versus carbon tax savings and other virtual
benefits in specific regions.

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